When I mark multiple mails (Shift+CursorDown) and delete the mails (Shift+Del) and after this I immediately press again one time Shift+CursorDown, multiple mails are now selected altough there should only be marked two of them.

It seems that somehow the number of deleted mails are still taken into account (some indexing mistake, ...)

Here's how to reproduce:
1. Send 3 messages to yourself. Check your mail and receive them. In your inbox (or whatever folder), they might look like this:
Test3
Test2
Test1
All 3 messages should be in the "unread" state.
2. Select the first message (Test3). Delete it. You'll note that, as is noble and good, the message Test3 disappears and now Test2 is selected. Yay!
3. Now comes the part that is less noble or good: hit "+" to go on to the next unread message. You'll note that _both_ Test2 and Test1 are now selected. If you hit delete, _both_ are gone. Rats!

The proper behavior would be that, after deleting Test3, only Test2 is selected, and when you hit "+" only Test1 should be selected.

I should also have specified: this bug is a great way to lose mail. If Test2 is a useful message you planned to keep, but Test1 is junk, when you try to delete Test1 you also lose Test2. I've definitely lost mails this way (and now that I know about the bug, I've fetched others out of the trash).

Thank you for taking the time to report this bug and helping to make Ubuntu better. We are sorry that we do not always have the capacity to look at all reported bugs in a timely manner. There have been many changes in Ubuntu since that time you reported the bug and your problem may have been fixed with some of the updates. It would help us a lot if you could test it on a currently supported Ubuntu version. When you test it and it is still an issue, kindly upload the updated logs by running apport-collect 511263 and any other logs that are relevant for this particular issue.

Thank you for your update on the matter.
For a next time: you can add the tracker by clicking on 'Also affects project' and copy/paste the (KDE) URL. So Launchpad is able to track the upstream changes.

KMail2 was released in 2011, and the entire code base went through significant changes. We are currently in the process of porting to Qt5 and KF5. It is unlikely that these bugs are still valid in KMail2.

We welcome you to try out KMail 2 with the KDE 4.14 release and give your feedback.